An Important Safety Tip for the Rudder Pedal Adjustment Rack

An Important Safety Tip for the Rudder Pedal Adjustment Rack

There are four pedal adjustment racks on the Stearman. (75-3409 –1&-2 or 75-3413), one for each side of both the front and rear rudder pedals. With the four position holes in each rack, one is able to adjust the forward and aft position of the rudder pedal. On the front racks, there are either one or two ¼ inch diameter holes in the extrusion just forward of the last 5/16 inch adjustment hole that accepts the pin on the bottom of the pedal assembly. Where there are two holes, the front hole is not used on the front rudder pedal location.

The ¼ in hole just in front of the most forward 5/16 inch pedal adjustment hole must have a bolt, an aluminum spacer, and a castle nut with a cotter pin installed. The head of the bolt and the spacer go on the inside of the extrusion, and the cotter-pinned nut goes on the outside. This bolt and spacer serves as a forward stop for the rudder pedal.

If this bolt is missing, and a pilot in the front cockpit depresses the toe tabs under the rudder pedals in order to move the pedals forward to get more leg room, and then pushes with his feet, the pedals can go whistling right off the front of the racks. This leaves the front cockpit with no rudder control. With the racks now sagging down in front digging into the aluminum fairings, the pilot in the rear cockpit is in for an exciting time if this should happen during flight. At my last count, I have seen four Stearmans with these critical bolts missing on both sides.

Often there is only the bolt and nut, and that serves the purpose. However, the aluminum spacer keeps the pedal mechanism from hitting into a sharp corner of the head of the bolt when the pedal is stopped at the limit of travel. Get in the habit of checking any Stearman that you come across for this stop bolt. While on the subject of the adjustment racks, here is a bit of information that may come in handy. Originally these extrusions had steel bushings with 5/16 inch ID, pressed into the four adjustment holes.

Two different kinds of bushings were used. One fit flush into the extrusion and required a countersink for the shoulder. Another bushing had a shoulder on the outside of the extrusion. Either of these configurations prevented the rudder pins from wearing the holes in the aluminum extrusion.

At some time, Boeing switched over to an extrusion that had the four 5/16 inch holes drilled in the aluminum extrusion with no bushings. These wear to an oblong hole after a while. Also, early on, there were two lengths of adjustment racks. The longer one, 75-3409-1 (9 7/16 inch) went on the front, and the shorter one (-2) (8 ½ inch) went on the rear. The front length is important because that is what contacts the phenolic stop to limit rudder travel and prevent extra stress on the rudder control arm. These two parts were made from the same extrusion piece, and the long one was cut off to create the shorter dash 2.

It fouls up the rudder travel adjustment to get the short one up front, or to get one of the four a different length from the other three. Boeing later went to a universal rudder rack (9 7/16 inch) length and one part # (75-3413) for both front and rear. The long ones on the rear require some adjustment in the lengths of the rear rudder cables.

Note: This subject was covered by Tony Farhat in a Technical Seminar at Galesburg. After the seminar there were three or four Stearmans on the field, identified with these bolts missing.

Fig.1 – Rudder Pedal Adjustment Rack With Stop Bolt in place.

By Jack Davis|
2016-11-13T09:32:50+00:00 July 26th, 2016|Flying-Wire|Comments Off on An Important Safety Tip for the Rudder Pedal Adjustment Rack

Stearman Restorers Association

The Stearman Restorers Association is an independent “Not for Profit” 501C-3 Corporation that is dedicated to the preservation, restoration, flying and safety of Stearman Aircraft through the education of both members and the public. The Stearman was a primary trainer for both Army and Navy cadets in WWII.